1. Technical Field
The present specification relates to a method and apparatus for manufacturing a toner, and a toner manufactured by the method and apparatus.
2. Description of the Background
In electrophotography, electrostatic recording, electrostatic printing, etc., a developer is adhered to an image bearing member such as an electrostatic latent image bearing member on which an electrostatic latent image is formed, transferred from the image bearing member onto a transfer medium such as paper, and finally fixed on the transfer medium.
As the developer configured to develop the electrostatic latent image formed on the image bearing member, a two-component developer, which includes a carrier and a toner, and a one-component developer consisting essentially of a toner (e.g., magnetic toner and non-magnetic toner) are known.
As a dry toner for use in electrophotography, electrostatic recording, electrostatic printing, etc., a pulverized toner, in which a toner binder such as a styrene resin and a polyester resin, a colorant, etc. are melt-kneaded and pulverized, is widely used.
Recently, polymerized toners manufactured by polymerization methods such as suspension polymerization and emulsion polymerization aggregation have gained attention. Published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 07-152202, for example, discloses a polymer dissolution suspension method. In this method, toner components are dispersed and/or dissolved in a volatile solvent such as an organic solvent having a low boiling point to prepare a toner component mixture liquid. The prepared mixture liquid is emulsified in an aqueous medium containing a dispersant to form droplets of the mixture liquid. Finally, the volatile solvent is removed from the droplets to prepare toner particles while contracting the volume of the droplets.
Unlike suspension polymerization methods and emulsion polymerization aggregation methods, the polymer dissolution suspension method has the advantage that various kinds of resins can be used. For example, a polyester resin, which is useful for obtaining a full-color image having transparency and smoothness, can be used for this method.
Since the polymerized toners are prepared in an aqueous medium containing a dispersant, the dispersant tends to remain on the surface of the toner particles, which degrades chargeability and stability of the toner particles, and removing the remaining dispersant requires large quantities of water. Thus, the polymerization methods are not necessarily satisfactory.
JP-A 57-201248 discloses a spray drying method that is well known as a method for manufacturing a toner without using an aqueous medium. In this method, a mixture of toner constituents in a melted state or a liquid in which toner constituents are dissolved is discharged from various atomizers as fine particles, and the fine particles thus discharged are dried to obtain toner particles. Because an aqueous medium is not required, the above-described problems can be circumvented.
However, the toner particles manufactured with the spray drying method are relatively coarse and large, and tend to have a larger particle diameter distribution, degrading the quality of the toner.
Japanese Patent No. (hereinafter referred to as JP) 3786034 discloses a method and apparatus for manufacturing a toner in which microdroplets of a toner constituent liquid formed by piezoelectric pulsation are dried and solidified to obtain toner particles. JP 3786035 discloses a method for manufacturing a toner in which microdroplets of a toner constituent liquid formed by thermal expansion in a nozzle from which the toner constituent liquid is discharged are dried and solidified to obtain toner particles.
In the apparatuses disclosed in JP 3786034 and JP 3786035, a gas flow feed means is provided. A gas supplied from the gas flow feed means is injected from each of one or more gas injection openings provided between head sections of an apparatus through a duct at a substantially constant pressure. Therefore, particles of the raw material intermittently injected from a discharge part of the apparatus are conveyed at regular intervals and solidified.
However, in the above-described methods and apparatuses, liquid droplets are discharged from a single nozzle by a single piezoelectric element. As a result, a number of liquid droplets discharged per unit of time is limited, decreasing productivity.
Moreover, a more complicated configuration is required to supply a gas to each discharging part. Furthermore, when a direction of discharge of the liquid droplets and a direction of a gas flow is uncontrolled, the liquid droplets initially discharged separately from the nozzle may be combined together, especially in an area where a frequency of piezoelectric pulsation exceeds 100 kHz.
To solve the above-described problems, the present inventors have proposed a method and apparatus for manufacturing a toner disclosed in JP-A 2006-293320, in which a nozzle is vibrated by expansion and contraction of a piezoelectric element serving as a vibration generating means, so that liquid droplets of a toner constituent liquid are discharged from the nozzle or nozzles at a constant frequency and solidified to form toner particles of generally uniform diameter. In addition, in JP-A 2006-297325, the present inventors have also proposed a toner manufacturing apparatus including a discharging member having discharge holes, and vibration means configured to apply vibration to the discharging member at a predetermined frequency. The discharging member is vibrated by the vibration means so that liquid droplets of a toner constituent liquid are discharged from the discharge holes, and are dried and solidified to form toner particles.
In JP-A 2006-293320, because the piezoelectric element is provided around the nozzle to vibrate the nozzle by expansion and contraction of the piezoelectric element, the nozzle is vibrated only in an area corresponding to an opening between adjacent piezoelectric elements, which somewhat limits vibration amplitude. Consequently, due to such more limited vibration amplitude the nozzle may be susceptible to clogging when toner constituent liquid having a high viscosity of, for example, 10 mPa·s, in which a large amount of solid components is dispersed, is discharged from the nozzle. Although a configuration thereof is not specifically described, the toner manufacturing apparatus disclosed in JP-A 2006-297325 provides almost the same effect as that of the method and apparatus for manufacturing a toner disclosed in JP-A 2006-293320, and therefore may be prone to the same type of problem.